Composite refractory lining for basic oxygen furnace



Dec 17 1958 F. CAMPBELL, JR

COMPOSITE REFRACTORY LNING FOR BASIC OXYGEN FURNACE Filed March l5, 1966lll/ll ll Fra/7K Cam/abe# z/r.

I NVENTOR United States Patent O 3,416,779 COMPOSITE REFRACTORY LININGFOR BASIC OXYGEN FURNACE Frank Campbell, Jr., Bethlehem, Pa., assignorto Bethlehem Steel Corporation, a corporation of DelawareContinuation-impart of application Ser. No. 482,680,

Aug. 26, 1965. This application Mar. 1S, 1966, Ser.

2 Claims. (Cl. 266-36) ABSTRACT OF THE DISCLQSURE A composite workinglining for va basic oxygen furnace including a first layer of sprayable:basic refractory bricks which may be one of the following types ofbasic refractory bricks: tempered tar-bonded, resin-bonded or coked,carbon-bonded tar impregnated; laid up against a layer of refractorymaterial protecting the shell of the vessel and a second layer ofnonsprayable basic refractory bricks which are burned andtar-impregnated laid up inwardly of said first layer of basic refractorybricks.

This invention in general relates to linings for metallurgical furnacesand in particular to llinings of furnaces utilizing oxygen as a means ofmelting and refining steel such as the basic oxygen furnace and is acontinuationin-part of my application Ser. No. 482,680, led Aug 26,1965, now abandoned.

A basic oxygen furnace shop usually consists of at least two furnaces.Economically, a one furnace shop is not feasible because of theexcessive down-time required to reline the furnace with refractory brickdecreasing the furnace availability of the shop. Relinng a furnacerequires at least three days and may require as much as seven days. Onthe other hand, theoretically, a two furnace shop will maintain acontinuous production of refined steel because of furnace availability.While one furnace is down for relining, the second furnace is availableto produce steel. When the down furnace has been relined and the liningburned-in, it is ready for operation and the operating furnace can betaken out of service for relining. The down furnace now becomes theoperating furnace and the operating furnace is now the down furnace.Alternating furnaces in this manner results in an economical, eiiicient,continuous operation. Unfortunately, this mode of operation is not oftenachieved because of early failure of the refractory brick lining in theoperating furnace resulting in downtime while waiting for the downfurnace to be relined and burned-in thus decreasing the furnaceavailability in the shop.

The basic oxygen furnace generally comprises a steel shell and the basicrefractory lining. The basic refractory lining includes a safety lining,usually burned magnesite brick laid-up against the shell of the furnace,an inner working lining of a tar-containing dolomite or magnesite brickand a rammed tar-containing magnesite mix between the safety lining andthe working lining.

The refractory brick lining in the basic oxygen furnace fails becausethe brick cannot withstand the severe varying conditions, for example,excessively high temperatures caused by reaction of the metal with highvelocity, gaseous oxygen, changing slag compositions, splashing causedby the introduction of oxygen at supersonic velocities, and erosioncaused by the impact of heavy raw materials during charging, which existin the furnace.

Because the basic oxygen process utilizes basic slags, the workinglinings, that is, the refractory brick lining which is exposed to thehot metal, are made of basic refractory materials, such as stabilizeddolomite, mag- ICC nesite or combinations thereof. In the prior art eachparticular lining of a furnace is made of one particular basicrefractory material. In an effort to increase the service life of theworking lining and to improve the efficiency of the multi-furnace shopby increasing furnace availability, attempts have been made to spray theexposed surface of the Working lining with a basic refractory mix ofhigh purity magnesite bonded with tar, pitch, or resin materials, whilethe furnace is being tilted after tapping. This has not always beensuccessful because the sprayed material does not adhere to all types ofbrick used in the working lining. Then too, the sprayed material maycause thermal shock in the brick of the working lining resulting inspalling of the face of the brick reducing the service life thereof.Also, because of the high heat of the furnace, it is difficult to locatethe areas which require spraying. As a result, areas which should besprayed may not be properly sprayed resulting in premature failure ofthe lining.

Other types of Ibasic refractory brick may not be sufficiently resistantchemically and physically to the varying compositions of the slagsformed by the reactions in the basic oxygen furnace. Premature failureof the working lining occurs. These brick do not have a service lifesufficiently long to allow relining of the down furnace while the secondfurnace is in operation, resulting in reduced furnace availability.

It is, therefore, the object of this invention to provide ametallurgical furnace with a working lining having improved servicelife, thereby increasing the furnace availability of the shop.

It is another object of this invention to Iprovide a metallurgicalfurnace with a composite working lining, one component of which willresist erosion at the high temperatures existing in the furnace and theother component of which will resist spalling when sprayed with arefractory mix.

These and other objects are attained by providing a basic oxygen furnacewih a working lining comprising several types of brick, each type ofbrick being selected for its physical and chemical properties accordingto the lconditions each type must meet.

In a multi-furnace shop, it is advantageous to use a spray maintenanceprogram. In this type of program, one furnace operates while the otherfurnace or furnaces are being relined or being sprayed. To make use of aspray maintenance program, it is necessary that the operating furnacehave a working lining which will wear a suliicient length of time toallow the relining and burning-in of the said working lining in thesecond furnace. It is further necessary that a sucient amount of theworking lining of the operating furnace remain so that by spraying thesaid working lining, the furnaces may be operated alternately therebyincreasing furnace availability which might thereby increase shopproductivity. The lining life of the operating furnace is prolonged byspraying it with basic refractory materials which Imust adhere to thebrick in the working lining without causing thermal shock and spallingin the lining.

The single gure of the drawing shows the general arrangement of therefractory working lining in a basic oxygen furnace contemplated in theinstant invention.

In the drawing, the basic oxygen furnace is shown generally at 10. Theshell of the furnace is designated by 11. Immediately adjacent to andlaid-up against the shell of the furnace is a basic refractory bricksafety lining 18 made from basic refractory brick such as burnedmagnesite, stabilized dolomite and the like. The dished bottom or centerdome shown at 12 is lined with a tar-containing refractory brick such asdead burned dolomite, dead burned lime, stabilized dolomite, magnesiteand the like either alone or combinations thereof. The stadium andoperating slag line area of the furnace shown at 13 is lined with atar-impregnated basic refractory brick such as magnesite and the like.Itis preferred to use a magnesite brick having a high percentage ofmagnesia, that is, up to 97% magnesia. The barrel or splash area showngenerally at 14 extends from the stadium and operating slag line 13 ofthe furnace up to the charging pad 15 at the base of the cone 21 of thefurnace. In this area, a layer of tempered tar-bonded or resin-bonded ora coked carbon-bonded tar impregnated basic refractory brick 17 of themagnesia or dolomite type is laid-up against the safety lining of thefurnace. An inner layer of basic refractory brick 16 which is exposed tothe molten metal and to the atmosphere within the furnace is laid-upagainst the basic refractory brick 17. The inner layer of basicrefractoiy brick 16 may be of the burned tar-impregnated type, such asmagnesite or stabilized dolomite but it is preferred to use the puremagnesite type of brick having up to 97% magnesia. The high puritymagnesia refractory brick is more highly resistant to the varyingcompositions of the slag and to d the FeO content of the slag than arethe dolomite refractory brick or the refractory brick containing lessthan 97% magnesite. Because this type of basic refractory brick isresistant to the slag compositions, has greater resistance to abrasionand erosion and has higher hot strength due to the ceramic bondingtherein than other types of basic refractory brick, the service life islonger than the other types of basic refractory brick.

The charging pad 15 of the furnace, so-called because the raw materialsimpinge on this area of the furnace wall when they are charged into thefurnace, is lined with burned tar-impregnated magnesite refractory brickhaving a high resistance to abrasion and erosion and high hot strength.

The upper zone 20 of the cone section 21 may be of tempered tar-bondedor resin-bonded basic refractory brick such as dead burned magnesite ordead burned dolomite or stabilized dolomite and the like, although it itpreferred to use a magnesite brick having at least 80% magnesia. Thefurnace is provided with a conventional refractory lined tab hole 19 inthe cone section 21.

When the burned tar-impregnated brick 16 wear down to expose the layerof tempered tar-bonded or resinbonded or a coked carbon-bonded tarimpregnated brick 17, the exposed surface of the tempered tar-bonded orresin-bonded or a coked carbon-bonded tar impregnated brick is coatedwith a layer of the aforementioned basic refractory spray mix. Theoperating sprayed furnace is then used alternately with the newlyrelined burned-in furnace. When the tempered tarabonded or resin-bondedor a coked carbon-bonded tar impregnated portion of the working liningof the operating furnace has been worn down to the safety lining, it isremoved from service for relining. A sucient portion of the burnedtar-impregnated basic refractory brick remains in the one furnace nowoperating, to allow the relining and the burning-in of the lining in theinoperative or down furnace. By using the spray maintenance program, itis therefore, possible to increase the service life of a working liningand thereby increase furnace availability of the Shop.

In a specific example of the invention, a 250 ton basic oxygen furnacewas lined with a safety lining of burned magnesite brick. The workinglining was made up of various tar-containing types of brick each brickbeing best adapted to be used in the particular area of the furnace. Thecenter dome is laid up with 24 x (6 to 51/2 and 6 to 5 and 6" to 4") x 3tar-bonded magnesia brick. The stadium and operating slag line area hasten rings of high purity magnesite, at least 97% magnesia brick eachbeing 27 x (6 to 51/2" and 6 to 4) x 3". The splash or wear area has 43to 47 courses of two types of brick. The layer of brick exposed to theslag splash are of burned tar-impregnated high purity magnesitecomposition, alternate courses of brick being l2" x (6" to 5]/2 and 6"to 5) x 3 and 15I x (6 to 51/2 and 6" to 5) x 3". The

intermediate layer of brick between the burned tar-impregnated brickabove and the safety lining is made of tempered tar-bonded magnesitebrick, alternate layers of which are 12 x (6'l to 51/2" and 6" to 5) x 3and l5 x (6 to 51/2 and 6 to 5) x 3". The brick in the splash area arelaid-up in overlapping relationship to each other. The base cone orcharge pad brick are burned tarimpregnated hmagnesite having a highresistance to abrasion and high hot strength. Each brick is 24" x (6 to51/2 and 6 to 4") x 3". The cone section ofthe furnace is lined withtempered and tar-bonded brick two sizes of brick being used, the lowerportion of the cone having brick 21 x (6 to 5%." and 6 to 5" and 6" to4) x 3" and the upper portion of the cone section having brick 18 x (6to 51/2 and 6 to 5" and 6l to 4) x 3".

The furnace was burned-in, and operated continuously to make 164 heats.A small wear area in the upper portion of the slag splash area wasnoted, that is, the burned tar-impregnated magnesite refractory brickhad worn through to the tempered tar-bonded brick. Because of anunavoidable delay in relining the down furnace which stretched therelining and burning-in of the down furnace to seven days orapproximately 4 days longer than normal time required, necessitating aone furnace operation, the spray program could not be started until 194heats had been made. At this time, the small wear area had enlarged andseveral other Wear areas were noted at the operating slag line and theturneddown slag lines. The wear areas were sprayed with approximately2600 pounds of Quigley type BOF guntapite (an 87% magnesia mix havingborate and phosphate bonding agents added). The furnace lining wassprayed intermittently until 255 heats had been made. At this point, thedown furnace was burnedin and operated alternately with the sprayedfurnace. At 255 heats the operating furnace was sprayed withapproximately 5200 pounds of the 87% magnesia mix. The operating furnacewas sprayed at 268 heats, 275 heats, 289 heats and 294 heats. The weararea at the operating slag line was noticeably larger and deeper and itwas noted that several brick from this area were dislodged and fell intothe molten metal. The furnace was sprayed after 298 heats, 308 heats,311 heats and 319 heats respectively. It was then noted that the safetylining was being eroded. The furnace was taken off operations forrelining.

By comparison, in a furnace having a working lining of temperedtar-bonded refractory brick only, a wear area at the operating slag linewas noted and sprayed after heats. The spraying technique allowed thefurnace to be used to make an additional 33 heats or a total of 213heats.

Since the composite lining and the spraying technique were responsiblefor increasing the production of the furnace from 194 heats to 319 heatswhereas an increase of only 33 heats was obtained by using the spraytechnique wtih a lining composed of only one type of brick, namely,tempered tar-bonded, it is evident that the use of the composite liningwill increase the efliciency of a multi-furnace basic oxygen shop byincreasing the furnace availability of that shop.

The wear of the basic refractory brick in the working lining is not eventhroughout the furnace. It has been found that areas of the Workinglining exposed to the more severe conditions wear more rapidly thanother areas. The brick in the Operating slag line, tapping slag line,splash area and charging areas wear more rapidly than the brick in otherareas of the working lining. The wear occurs as a crater or hole in thelining. These areas are usually difcult to observe because of theintense heat in the furnace. It has been found that the uneven wear ofthe burned tar-impregnated refractory brick of the composite lining ofthe invention creates a washboard like pattern which is readilydiscernible when the furnace is tilted for pouring or charging. Theappearance of the Washboard pattern indicates that spraying is requireda group consisting of tempered and tar-bonded basil and pinpoints theareas which should be sprayed. When refractory bricks, resin-bondedbasic refractorj the wear surface becomes smooth and the washboardbricks, and coked carbon-bonded tar impregnatec pattern can no longer beseen, the burned tar-impregnated basic refractory bricks, and refractorybrick have been worn away and the remaining 5 (b) a second layer ofburned tar-impregnated basic refractory lining is tempered tar-bondedrefractory brick. refractory bricks laid inwardly of said first layer oiAlthough I have shown the splash area of the working basic refractorybricks. lining in the furnace, laidup wtih overlapping courses 2. Acombination as claimed in claim 1 in which said 0f brick, it is withinthe scope of this invention to laysecond layer of basic refractorybricks is in alternate up this area with the faces of the brick inabutting relalo course-overlapping relationship with said first layer oftionship. It is also within the scope of this invention to basicrefractory bricks. use a Working lining of greater or lesser thicknessthan disclos-ed in this specification depending upon the severityReferences Cited OfIthle praatten. UNITED STATES PATENTS c aim: 1

1. A basic oxygen vessel having a metal shell, gen- 5 248-0359 8/1949Debnham 26643 erally dening a bottom zone a barrel zone and a cone3141790 7/1964 D iwles et al' 266`43 3,294,386 12/1966 Wlllenbrock266`43 Zone, a shell protective lining in contact with the insidesurface of the shell and an improved composite working J SPENCEROVERHOLSER Pfl-mary Emmi-nPr lining substantially throughout said barrelzone in contact 20 v with and subjected to attack by the environment insaid R- D BALDWIN, Assistant Examine"- basic oxygen vessel, said workinglining comprising:

(a) a first layer of bricks capable of being sprayed U-S- Cl- XR- with abasic refractory material, laid against the 266-43 shell protectivelining, said bricks being selected from 25

